Research Journal of Applied Sciences, Engineering and Technology 2(6): 504-507, 2010
ISSN: 2040-7467
© M axwell Scientific Organization, 2010
Submitted Date: November 02, 2009
Accepted Date: December 07, 2009
Published Date: September 10, 2010
Evaluation of the Effective Baking Conditions for Grade 3 Nigerian
Acacia Species Bonded Foundry Sand Cores
1
1
Nuhu A. Ademoh and 2 A.T . Abdullahi
Department of Mechanical Engineering, Nigerian Defence Academy,
P. M. B 2109, Kadu na, Nigeria
2
Department of Mechanical Engineering, Bayero University, Kano
Abstract: The most effective economical baking conditions w ere determine d for foundry cores bonded with
the grade 3 Nigerian acacia species exudates. Silica sand base cores bonded with the material were oven baked
at temperatures ranging from 160 to 250ºC for varying pe riods oven cooled and then subjec ted to ten sile
strength tests to ascertain the best baking co nditions for different alloy ca stings. The ex perimental core
specimens were in accordance with foundry test standard, shaped like figure number eight. They were tested
with standard universal strength machine equipped with attachment for gripping the cores and an instantaneous
meter from which the test values w ere read. The result were compa red with estab lished standard foundry core
property table which showed that the class V iron/steel cores are best made with 3% acacia bonded silica sand
baked at 160ºC for 1 h. For magnesium cores, sand bonded with 4.5% acacia baked at 160ºC for 1-2 h was
optimum. For class IV iron/steel cores 4.5% acacia bon ded sand baked at 180ºC for 1 hour was optimal. Sand
bonded with 4 .5% grade 3 acacia baked at 200ºC for 1.0-2.0 h was optimum for copper, aluminium, classes II
and III iron/steel cores. Sand bo nded w ith 8.0-13.0% grade 3 N igerian acacia sp ecies bake d at 200ºC for 1.5-2
h was found m ost effective for class I iron and steel cores.
Key w ords: Acac ia grade 3, bak ing, cores, oven , temperature
INTRODUCTION
Acacia species is a natural resin that contains arabin;
a semi-solidified sticky fluid that oozes from incision
made on ba rk of acacia tree s (Fen nem a, 199 6). Nigeria
produces four grades of acacia species exudates in
commercial quantities some of which are exported for
foreign exchange earnings. Grad es 1 and 2 acacia are
preferred by major importer countries of USA and Europe
that use it in food, beverage, pharmaceutical,
confectionary,
textile
and printing industries
(Rahim et al., 2007). This creates a research gap to find
industrial uses for grades 3 and 4 acacia species like using
it in other sectors like foundries that lack cheap sources of
good binders. Ademoh and Abdullahi (2009) tried the
grade 3 Nigerian acacia exudates as sole binder for sand
mou ld and it was found suitable at 6-9% compositional
content for non -ferrous and grey iron casting at co ntent.
The use of acacia species in foundry core production
include addition of 5% acacia spec ies exu dates gum to
10% sugar and protein in gelatinous a mix derived from
amino acid for binding expendable cores for casting
(Siak et al., 1994). Acacia gum com bined with sugar, urea
formaldehyde resin and boric acid to bind cores
(Eric, 1965). These processes inv olve u se of acids to
enhance core performance. Other processes free of acids
use corrosive organic, inorganic resins and chemicals,
which are toxic to human and involve multiple process
stages that imply additional costs for safety precautions.
This coup led w ith defects like porosity, cavities and
pinholes caused by evolved gases entrapment require that
simpler, non-hazardous processes that generate less gas
and defects are developed to assist small scale and less
advanced foundries especially in the developing countries.
The aim of this paper is to determine the most
effective bakin g temperatu re and time for Nigerian acacia
species grade 3 bonded cores. The objectives are to
measu re tensile strength of cores bonded w ith acac ia
grade 3 baked at 160, 180, 200, 220 and 250ºC for 1-3 h,
test them for tensile strength; permeability and shatter
index and compare result with the standard in Table 1
(Titov and Stepanov, 1982), to determine the optimal
baking conditions for such sand cores. The significance is
that foundries that use the material in oven baking process
for core production would be properly guided on the most
effective and eco nomica l operating conditions for best
results.
MATERIALS AND METHODS
Silica sand sample with clay content of 0.3% was
used to prod uce the core test specimens. The sand was
oven dried at 110ºC to remove free water, weighed and
transferred to a mechanical sieve and vibrated for about
Corresponding Author: Dr. Nuhu A. Ademoh, Department of Mechanical Engineering, Nigerian Defence Academy, P.M. B 2109,
Kaduna, Nigeria
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Res. J. Appl. Sci. Eng. Technol., 2(6): 504-507, 2010
Table 1: Desired physical properties ranges of sand cores
Alloys
Permeability (No)
Ten sile streng th (K N/m 2)
Class I iron/steel cores
130-150
700-1000
Class II iron/steel cores
100
500-700
Class III iron/steel cores
100
350-600
Class IV iron/steel cores
70
200-300
Class V iron/steel cores
70
80-150
Copper bronzes cores
90
400-600
Copper brasses cores
60
500-700
Aluminium co res
80-100
400-700
Magn esium cores
80
300-500
30 min for grain size distribution (AFS , 1989). A quantity
of sieved sand of BS standard grain size of 40-72 meshes
was taken and used to produce specimens. The grade 3
Nigerian acacia species exudates was milled to grain size
corresponding to BS sieve of 30 mesh for prop er particle
mix and bond reaction. The sand and acacia exudates
were thoroughly mixed in a roller mill for 10 min and
moulded into core specimen in accordance with the
research test schedule. The tensile strength specimen was
in accordance with usual foun dry standard mo ulded in
split core box to shape like figure number eight (Busby
and Stancliffe, 1997). They were rammed with three
compacting blows each weighing 6.5 Kg dropped from a
50 m m he ight.
After oven baking specimens at 160, 180, 200, 220
and 250ºC for periods of 1-3 h, they were oven cooled and
tested with standa rd universal strength equip ped with
attachment to grip sp ecimen an d me ter that read tensile
strength instantaneously (AFS, 1989). Permeability and
shatter index specimens were cylindrical in shape,
measured 50 mm diameter by 50 mm height and weighed
130 g after ramming with three compaction blows each of
6.5 Kg dropped from 50mm height with a standard sand
ramm er. These are the most critical mechanical properties
of cores that determ ine their performance in practice
(Titov and S tepan ov, 19 82; D ietert, 196 6). For tensile
test, a steadily increasing tensile force was applied on
core specimen by universal strength machine until failure
just occurred and the strength was read instantaneously.
For the green permeability test, standard air pressure of
9.8x102 N/m 2 was passed through the specimen in the
sample tube placed in meter and after 2000 cm 3 of air
passed through it, perme ability was read (Dietert, 1966).
Shatter specimen placed in container of the test machine
was push ed up wards ov er strippin g post until it struck
anvil, fell and shattered. Retained sand and over size were
collected, measured and automatically used by machine
to compute shatter index read instantaneously from the
meter.
Fig. 1: Green Permeability and shatter index (No) of foundry
sand cores bonded with varying percentages grade 3
Nigerian acacia species
DISCUSSION
The results of green permeability and shatter index
tests are as presented in Fig. 1. Permeability was observed
to decrease from 201.0No at 3% acacia binder to 143.5No
at 13% acacia binder content. The trend is explained by
the fact that increase in binder led to increased
compaction and decreased porosity for gas escape. The
permeability was compared to the standard in Table 1
showed that the material is suitable at all compositions
investigated for all classes of sand cores for different
alloys. Shatter index decreased with increased binder
because more binder imposed higher bonding and less
collapsibility of sand cores. However the values are
adeq uate for all classes of cores.
Figure 2 presented the result for cores bon ded with
grade 3 acacia ba ked at 160 ºC for 1-3 h. When com pared
with foundry standard in T able 1, it show s that 16 0ºC is
the optimum baking temperature for classes IV and V iron
and steel cores, 1 h is the optimum ba king period for class
V cores and 2.5-3.0 h for class IV iron and steel cores. For
magnesium and class III iron and steel cores, sand bonded
with 4.5% acacia baked for 1-2 h is the optimum. For
bronze and aluminium cores optimum baking period at the
same composition is 1.5-2.0 h. Cores bonded with 11.513% acacia baked at 160ºC for 1.5-2.0 h is most effective
for brass, class II iron and steel castings.
RESULTS
Figure 1-6 presents the experimental results of
research in graphical plots. Figure 1 presents the result of
green perm eability test. Figure 2-6 present the results of
the tensile strength specimen’s oven baked at 160, 180,
200, 220 and 250ºC for of 1-3 h, oven cooled and then
tested as described above. Tensile strength is the most
critical of the properties of cores and it measured their
ability to withstand the rupture stresses imposed on them
by thermal expansion during casting . Perm eability
measured the ease of escape of gas from sand cores
during casting, while shatter index measured the
collapsibility of core after casting for easy fettling and
cleanliness.
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Res. J. Appl. Sci. Eng. Technol., 2(6): 504-507, 2010
Fig. 4: Tensile Strength (KN/m2) of sand cores bonded with
varying percentages grade 3 Nigerian acacia species
baked at 200ºC for varying periods in hours
Fig. 2: Tensile Strength (KN/m2 ) of sand cores bonded with
varying percentages grade 3 Nigerian acacia species
baked at 160ºC for varying periods in hours
Fig. 3: Tensile Strength (KN/m2) of sand cores bonded with
varying percentages grade 3 Nigerian acacia species
baked at 180ºC for varying periods in hours
Fig. 5: Tensile Strength (KN/m2) of sand cores bonded with
varying percentages grade 3 Nigerian acacia species
baked at 220ºC for varying periods in hours
The result for core specimens baked at 180ºC is
presented in Fig. 3. Just as observed in Fig. 2 tensile
strength of baked cores increased with increasing binder
and baking period because the two baking temperatures of
160 and 180ºC are below the melting point of material
above which it will begin to burn off and weaken strength.
The grade 3 Nigerian acacia melts at 184-188ºC
(Eric, 1965). The result in Fig. 3 when com pared with
Table 1 show that 3.0% acacia bonded sand is optimum
for class IV iron an d steel core w hen it is baked a t 180ºC
for 1-3 h. 4.5% acacia bonded sand baked for 1-3 h at
180ºC is optimum for copper, aluminium and classes II
and III iron and steel cores; while 9-13% acacia bonded
cores baked at 1.5-3.0 h is optimum for class I iron and
steel cores.
Figure 4 presented tensile strength test result for
cores specimens bonded with grade 3 acacia baked at
200ºC for 1-3 h. Cores strength increased with baking
time for each acacia binder composition up to a baking
time of 2.5 h from w here strength decreased with baking
period because above the m elting point (184-188ºC)
prolonged holdin g of the material caused so me acacia
binder to burn off from cores resulting to weakening of
strength. In comparison with Table 1, the result shows
that sand bonded with 3 .0% acacia baked for 1 .0 hou r is
suitable for class IV iron and steel cores; that with 4.5%
acacia binder bak ed for 1.0-2.0 h is effective for copper,
aluminium and classes II and III iron and steel cores while
8.0-13.0% acacia bonded sand baked for 1.5-2 .5 h is
optimum for class I iron and steel casting co res.
Figure 5 and 6 presented tensile strength test results
for cores specimens bon ded with grade 3 acacia baked at
506
Res. J. Appl. Sci. Eng. Technol., 2(6): 504-507, 2010
different alloy castings at specified compositions, baking
temperatures and time for best result. The effective baking
condition determ ined in the stud y is vital as it prevents
unnecessary waste of time, material and energy and
lowers production cost. When com pared with the
chem ically based core processes (Rahim et al., 2007;
Siak et al., 1994), this work produced good sand cores
with simpler materials and method.
REFERENCES
Ademoh, N.A. and A. Abdullahi, 2009. Determination of
mechanical properties of m ould sand bonded with
grade 3 Nigerian acacia species. Int. J. Appl. Eng.
Res., 4(10): 1903-1910.
American Foundry Men Society (AFS), 1989. Mould and
Core test Handbook. 2nd Edn., Procedure, 113:
74-78.
Busby, A.D. and M.R. Stancliffe, 1997. Lies, Damned
Lies on Sand Testing. British Foundry Men, London.
90(2): 35-46.
Dietert, H.W., 1966. Foundry Core Practice. 3 rd Edn.,
American Foundry M en’s Society, Des Plaines, Inc.,
pp: 2-154.
Eric, P., 1965. USA Patent 3182030-Core binder
composition com prising sugar, gum Arabic, urea
formaldeh yde and b oric acid. 4 M ay.
Fennema, O.R., 1996. Food Chemistry. 3rd Edn., Marcel
Dekker Inc., New Y ork, pp: 60-82.
Rahim, A.H., E.C. Ierland and H.P. Weikard, 2007.
Competition in gum Arabic: G ame theoretic
mod eling approach. afaf.rahim @wur.nl.
Siak J.S., R.M. Schreck and K. Shah, 1994. USA Patent
no: 5320157. Expendable core for casting processes.
14 Ju ne.
Titov, N.D. and Y.U. Stepanov, 1982. Foundry Practice
Translated by Iva nov. P.S. M ir Publishers, Moscow,
pp: 49-101.
Fig. 6: Tensile Strength (KN/m2) of sand cores bonded with
varying percentages grade 3 Nigerian acacia species
baked at 250ºC for varying periods in hours
220 and 250ºC for 1-3 h, respectively. In Fig. 5 there was
marg inal increase in strength from baking period of
1-1.5 h follow ed by rapid decrease in co re bon d strength
with increased baking duration. This trend was caused by
over baking of cores at a temperature in excess of what
was required. Acacia species exudates as a class 3 type of
binder that melts and flows to form strong bonds w ith
sand when cooled to low temperature would perform best
at just above its melting range. Therefore, the 220ºC
baking temperature appears excessive for optimum
performance of material. The situation in Fig. 6 is even
worse than that in Fig. 5 as tensile strength followed trend
of slopping continuously from 1-3 h o f bakin g due to
similar reason of over baking cores. Thus cores bonded
with grade 3 acacia exudates are not to be baked at or
above these two temperatures.
CONCLUSION
The grade 3 Nigerian acacia species exudates has
been shown to be suitable for binding sand cores for
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